packetlife.net

by Jeremy Stretch

v2.0

IP

V

4 M

ULTICAST

Layer 2 Addressing

224.0.0.0/24

Group Ranges

224.0.1.0/24

232.0.0.0/8

233.0.0.0/8

Local network control

Internetwork control

Source-specific

GLOP (RFC 3180)

239.0.0.0/8 Admin-scoped

IGMP Configuration

ip multicast-routing

!

interface FastEthernet0/0

ip pim {sparse-mode | dense-mode | sparse-dense-mode}
ip pim version {1 | 2}

Distribution Trees

Source-Rooted
Provides the shortest paths from the
source to receivers

Shared
A common set of links which carry all
multicast traffic; statically configured

IGMP Troubleshooting

show ip igmp

show ip igmp group

224.0.0.1

Common Groups

224.0.0.2

224.0.1.39

224.0.1.40

All hosts

All routers

Cisco RP Announce

Cisco RP Discovery

IGMP

IGMPv2
Adds support for dynamic leave requests
and querier election to original IGMP

IGMPv3
Adds multicast source filtering to v2

IGMP Snooping
A switch passively inspects IGMP
requests to determine which hosts
should receive multicast traffic

show ip igmp interface

show ip igmp snooping

ip igmp join-group

Terminology

Internet Group Management Protocol (IGMP)
Hosts send IGMP requests to local routers to join multicast groups

Reverse Path Forwarding (RPF)
Verifies that multicast traffic travels in the reverse direction of
unicast traffic, away from the tree root

Cisco Group Management Protocol (CGMP)
A proprietary protocol used by switches to obtain multicast
membership information for end hosts (deprecated)

IGMP Support

IGMP Snooping

Router(config-if)# ip igmp [version <#>]

Switch(config)# ip igmp snooping

Protocol Independent Multicast (PIM)

Dense Mode
The initial tree encompasses all multicast routers; after a period of
time, routers without IGMP members prune back branches

Sparse-Dense Mode
Allows a PIM-enabled interface to function in either sparse or dense
mode per group

Sparse Mode
The tree is grown from a central rendezvous point out to the
multicast source and recipients

PIMv1
Provides automatic RP discovery with Auto-RP (Cisco proprietary)

PIMv2
Automatic RP discovery is accomplished by the bootstrap router
(BSR) method (standard)

PIM Configuration

RP Configuration

Manual

Auto-RP Mapping Agent

ip pim rp-address <IP>

ip pim send-rp-discovery scope <TTL>

Auto-RP Candidate

BSR Candidate

ip pim send-rp-announce <interface>

ip pim bsr-candidate <interface>

BSR RP Candidate

ip pim rp-candidate <interface>

PIM Troubleshooting

show ip mroute

show ip pim interface

show ip pim neighbor

show ip pim rp [mapping]

show ip rpf <IP>

IGMPv1
Original IGMP specification

239.142.57.6

01-00-5E-0E-39-06

11101111 10001110 00111001 00000110

00000001 00000000 01011110 00001110 00111001 00000110